Sure alot of absolute principles being tossed around in this thread.
Maybe we should take a closer look at the specs of the M80 again before talking about power requirements whether tube or SS. At 95db/91db/w/m the M80s are reasonably sensitive speakers that don't require much power to play at orchestra level volumes assuming normal listening room distances from the speakers. A 75 watt tube amp would not be stressed driving the M80s except at earsplitting peaks north of 105 db or very loud transients where the soft clipping of the tubes would be much more pleasant than the square wave distortions from SS clipping.
Whether one prefers the sound of tubes or SS is a matter of personal preference. Personally I've enjoyed the sound of the M80s with tubes as much as SS but that's just me. I wouldn't recommend using less than a 75 watt tube amp with the M80s but that would depend on your listening habits and room requirements.
